External Gas Controller For Tankless Water Heater

ABSTRACT

This invention is directed to maintaining the output water temperature of a tankless water heater to a constant temperature regardless of changes in water flow rate and/or changes in the temperature of the cold water feed. The water heater has a cold water feed pipe, a fuel line and a hot water output pipe. A temperature monitor attached to the water output pipe generates a signal which varies in direct proportion to the changes in water temperature of the heated water. This signal commands the control motor which operates a fuel valve. The valve then in turn controls the amount of fuel to the water heater. In operation, as the temperature of the hot water changes, the control motor operates the fuel valve to feed more or less fuel to the water heater, maintaining a more constant water temperature regardless of the water flow rate or the incoming water temperature.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a tankless water heater and more specifically to apparatus for heating water in a tankless water heater where a temperature monitor which is coupled to a control motor monitors the temperature of the hot water as it leaves the tankless water heater through an external output pipe of the water heater. Depending on the monitored temperature of the water, a control motor opens and closes a gas valve to increase and decrease the flow of gas to the tankless water heater to provide a stream of constant temperature hot water regardless of flow rate or the temperature of the cold feed water. In the present invention the gas valve which is an off the shelf item and the monitor and stepper motor are each located external to the tankless water heater and can be installed on any inexpensive tankless water heater.

2. Description of Related Art

Water heaters that monitor the temperature of the water and control the flow of gas to the water heater are known in the prior art. More specifically, by way of example, U.S. PreGrant Publication No. 2010/0133258 to Fima discloses a system that monitors a relief valve coupled to a water heater to limit the energy and water wasted resulting from the relief valve's failure.

U.S. PreGrant Publication No. 2009/0129763 to Cabrera discloses a sensor which measures the temperature of water flowing through a pipe prior to heating and a sensor for measuring the flow rate of water flowing through the pipe. A microprocessor receives as input the temperature of water flowing through the pipe prior to heating, the flow rate of water flowing through the pipe, and a set point for a temperature of heated water.

U.S. Pat. No. 7,164,851 to Sturm, et al. discloses a central processing unit (CPU) with an operating program and a plurality of water heater elements coupled to the CPU which is programmed to individually activate one of the water heater elements to a predetermined power level in response to a demand for heated water.

U.S. Pat. No. 6,552,283 to Cabrera, et al. discloses a flow switch for tankless water heaters having a relay switch which, when activated, signals to the water heater that hot water is required which in turn activates heating elements of the water heater. When the flow in the pipe subsides the water heater is deactivated.

U.S. Pat. No. 6,257,871 to Weiss, et al. discloses a thermopile for controlling a damper and a main burner valve within a gas-fired appliance. A control circuit includes a temperature which determines that the temperature of water or air is below a predetermined temperature a motor opens the damper and a valve.

U.S. Pat. No. 5,504,306 to Russell, et al. discloses a tankless water heater which senses a water outlet temperature and controls AC power through an on/off mechanism to regulate power to heating elements embedded in the water stream. A microprocessor performs a proportional, integrating and derivative calculation which are used to determine the operating characteristics of the heating system and to control the heating system.

U.S. Pat. No. 5,322,216 to Wolter, et al. discloses an electronic sensing device which senses an outlet water temperature of a heater, and a another electronic sensing device which senses a midway water temperature of the heater. The burner output is controlled to maintain a desired outlet temperature which is based on changes in water flow and incoming water temperature.

U.S. Pat. No. 4,970,373 to Lutz, et al. discloses an electronic temperature control system for a tankless water heater. The control system has comparison circuitry for comparing the difference between a water temperature selected from a temperature selection device and an actual water temperature sensed by a temperature sensing device.

U.S. Pat. No. 4,700,886 to McGhee, et al. discloses a control which utilizes sensed gas pressure downstream of a thermostat controlled valve as an indication of heat demand. A low limit transducer maintains adequate heated water for casual uses without excessive burner cycling. A flow transducer switches a thermostat from a low limit set point to a high limit.

SUMMARY OF THE INVENTION

In an exemplary embodiment of the present invention, there is disclosed apparatus for maintaining the output water temperature of a tankless water heater at a constant temperature with changes in water flow having a water pipe for feeding cold water to the water heater, a gas line for feeding gas to the water heater and a water pipe for carrying hot water from the water heater. A control valve is coupled to the gas line to control the flow of gas to the water heater, a control motor is coupled to the control valve to control the flow of gas to the water heater and a temperature monitor is coupled to the water pipe for carrying hot water from the water heater. The temperature monitor generates a signal that is fed to the control motor which varies as the water temperature from the water heater varies. In operation, as the temperature of the hot water changes, the control motor operates the gas control valve to feed more or less gas to the water heater to maintain a constant water temperature regardless of the rate of water flow or the temperature of the cold water.

The more important features of the invention have thus been outlined in order that the more detailed description that follows may be better understood and in order that the present contribution to the art may better be appreciated. Additional features of the invention will be described hereinafter and will form the subject matter of the claims that follow.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

The foregoing has outlined, rather broadly, the preferred feature of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention and that such other structures do not depart from the spirit and scope of the invention in its broadest form.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and advantages of the present invention will become more fully apparent from the following detailed description, the appended claim, and the accompanying drawings in which similar elements are given similar reference numerals.

FIG. 1 is a diagram of a tankless water heater that provides a flow of constant temperature water regardless of the volume of the water flow or the temperature of the cold feed water.

DESCRIPTION OF THE PREFERRED EMBODIMENT

There are several different types of tankless water heaters that significantly vary in price ranges. There are water heaters that have a feedback loop built-in to monitor output water temperature and other tankless water heaters that do not have a feedback loop to monitor output temperature for heating fuel source control purposes. Tankless water heaters without a feedback loop do not have an automated way to compensate for the seasonal variations in ground temperature that affect the water going to the tankless water heater. Therefore, in order to maintain a desired output temperature of the water throughout the year, a user has to manually adjust the flow of gas for heating the water.

The present invention is an external water sensor, external electromechanical controller and external gas flow valve which can be added to any tankless water heater to provide a water heater which automatically controls the gas flow to maintain the water temperature at a constant temperature regardless of the flow rate or the temperature of the cold feed water.

Referring to FIG. 1, there is shown a schematic diagram of a system 10 for providing a flow of constant temperature water regardless of the rate of water flow or the temperature of the cold feed water. In a preferred embodiment, an instantaneous tankless water heater 12 which uses gas to heat the water is connected to an inlet pipe 14 which supplies cold feed water to the tankless water heater. The water heater is also connected to a gas line 16 which supplies natural gas, propane or any other liquid or gas fuel to the water heatrer.

Two valves are located on the water heater 12. One valve is a manually adjustable valve 18 which is connected to the cold water inlet pipe to control the flow of cold water to the water heater. The other valve is a manually adjustable valve 20 which is connected to the fuel line to control the flow of gas to the water heater. The manually adjustable gas valve 20 is set to heat the cold feed water which is fed to the tankless water heater to a desired temperature of, for example 120 degrees F., when hot water is being drawn from the heater at a specific flow rate through outlet pipe 22 when, for example, a dishwasher or a cloths washer is operating. Thus, when a person in the household draws hot water while showering at the same time that the dishwasher or the cloth washer is also operating, the person showering will not receive a continuous flow of constant temperature hot water. Another problem is that the temperature of the cold feed water to the water heater will be different in the summertime than it is during the winter time. For example, the reasons for changes in the water temperature from a particular desired set point can include but is not limited to changes in water flow or changes to the water temperature going into the water heater which is caused by changes in the seasons pre-heating of the ground that the water flows through to different temperatures. In the summertime the cold feed water may be as warm as eighty degrees F. and in the winter time the cold feed water may be as cold as forty degrees F. Having a feedback system can defend against any reason that could cause the water heater to heat the water to the wrong temperature

The invention here disclosed is an add on external gas controller for tankless water heaters which will automatically compensate for various flow rates of cold feed water and will also automatically compensate for temperature changes in the cold feed water by increasing or decreasing the flow rate of the gas to the water heater to provide a flow of hot water which has a constant temperature regardless of the rate of flow of the water and the temperature of the cold feed water.

A temperature sensor 24 is coupled to the hot water outlet pipe 22 to monitor the temperature of the water as it leaves the tankless water heater. The temperature sensor does not monitor the water temperature within the water heater. The temperature sensor used to measure the temperature of the water from the water heater can be a thermo coupler, a thermistor, a digitized integrated circuit sensor, a non-contact sensor that uses infrared or laser measuring means, a solid state temperature sensitive transistor, a solid state IC. etc. The output signal from the temperature sensor is a voltage which varies as the temperature of the hot water varies. The output signal from the sensor is fed to a motor which could be a stepper motor, a servo motor, a geared motor, a solenoid, a muscle wire that is coupled to control the fuel valve or any device that can control a fuel valve which is located in control box 26. A standard electrical plug adapted to be plugged into a standard 115 volt AC wall outlet is connected to a step down transformer and a rectifier to provide a potential of 5 Volts DC which is the source of power to the control box 26. It is understood that the required source of power to the control box can be obtained from a 220 voltage source, a solar cell, a battery, or be powered off of a 3V power source, a 12V system or a 24V system. The electromechanical device such as a stepper motor located in the control box is connected through a connecting rod 28 to the control lever 30 of a fuel valve such as a gas ball valve 32 which is located in the gas line 16. The fuel valve 32 is not limited to a gas ball valve but can be any gas valve that can be adjusted to different positions which can limit the fuel flow to the water heater in small increments. Thus, depending on the value of the voltage that is fed to the stepper motor from the temperature monitor, the connecting rod will operate the control lever on the ball valve to control the flow of gas to the tankless water heater to provide a stream of hot water of a substantially constant temperature regardless of the flow rate of the water or the temperature of the feed water to the water heater.

In an embodiment a logic device can be coupled to the water temperature sensor and the fuel valve to prevent oscillations in water temperature. The logic device can be a microcontroller, a microprocessor, a CPLD, a FPGA, or other device with capabilities to translate sensory inputs into signals and send the signals to the electromechanical device for controlling the fuel entering the tankless water heater.

In an embodiment, the combination of the stepper motor and the gas valve can be replaced with commercially available gas valves that allow variable adjustment of the energy source for tankless water heaters.

In another embodiment a sensor can be located to monitor the water temperature prior to entry into the water heater and/or one of more sensors can be located to measure the flow of water through the pipes.

It is understood that this invention, although disclosed as using inexpensive easily obtainable components, can use any type of device that can monitor the temperature of the water coming out of the water heater and can make the necessary adjustments to the energy source going to the water heater without making any modifications to the water heater itself.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to the preferred embodiments, it will be understood that the foregoing is considered as illustrative only of the principles of the invention and not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are entitled. 

What is claimed is:
 1. Apparatus for maintaining a constant output water temperature of a tankless water heater where output water temperature changes can occur due to changes in incoming water temperature or changes in water flow rate comprising: a control valve coupled to a fuel line source to control the fuel flow to the water heater; an electromechanical device used to control the position of the fuel control valve; and a temperature sensor that produces an electrical signal which relates to the temperature of water to command the electromechanical device; wherein the control valve, the electromechanical device and the temperature sensor are coupled th external components of the tankless water heater.
 2. The apparatus of claim 1 wherein the control valve is a modulated fuel valve.
 3. The apparatus of claim 2 wherein the fuel valve is located to control the flow of fuel before the fuel reaches the water heater.
 4. The apparatus of claim 1 wherein the temperature sensor is coupled to monitor the temperature of the water as it leaves the tankless water heater.
 5. The apparatus of claim 4 wherein the temperature sensor is a thermistor, a thermo coupler, an infrared detector, a solid state temperature sensitive transistor, or a solid state IC.
 6. The apparatus of claim 1 wherein the electromechanical device is coupled to control the control valve.
 7. The apparatus of claim 6 wherein the electromechanical device is a stepper motor, a servo motor, a geared motor, a solenoid, or a muscle wire that is coupled to control the fuel valve.
 8. The apparatus of claim 1 wherein the fuel in the fuel line is natural gas, or propane, or any other liquid or gas fuel source.
 9. The apparatus of claim 1 wherein the temperature monitor, the control motor and the fuel control valve are adapted to be coupled external to the tankless water heater of the type without a built in feedback control loop.
 10. The Apparatus of claim 1 wherein a logic device is coupled to the water temperature sensor and the gas valve to prevent oscillations in water temperature.
 11. The apparatus of claim 10 wherein the logic device is a microcontroller, a microprocessor, a CPLD, a FPGA, or other device with capabilities to translate sensory inputs into signals and send the signals to electromechanical devices for controlling the fuel entering the tankless water heater. 